The vSphere SDK for Perl provides an easy-to-use Perl scripting interface to
the vSphere API. SDK ships with utilities, and documentation for building
vSphere management applications.

The vSphere Command-Line Interface (vSphere CLI) command set allows you to
run common system administration commands against ESX/ESXi systems from any
machine with network access to those systems. You can also run most vSphere
CLI commands against a vCenter Server system and target any ESX/ESXi system
that vCenter Server system manages.

vSphere CLI commands are especially useful for ESXi hosts because ESXi does
not include a service console.

WWW: http://communities.vmware.com/community/vmtn/server/vsphere/automationtools/vsphere_cli